1. Field of the Invention
The present invention relates to a rotary encoder contact disk capable of converting a rotational movement of its axis into a pulse signal to sense the angular position of the axis of the rotary encoder, and to a method for manufacturing the same.
2. Description of the Prior Art
A rotary encoder contact disk has hitherto been generally embodied as a laminated structure comprising at least three conductive layers and two insulating film layers sandwiched between the formers, formed on an insulative substrate. It usually requires at least five printing steps to be completed as shown in the attached drawings and will be discussed first as follows referring to FIGS. 1 to 5.
FIG. 1 is a plan view of the conventional rotary encoder contact disk. In the drawing, a substrate 1 of insulative material has a conductive layer 2 of internal gear-pattern thereon, another conductive layer 3 of ordinary gear-pattern and an annular conductive layer 4 of a planar slip-ring. Numerals 5, 6 and 7 designate terminal parts, in which the terminal parts 5 and 7 are electrically connected to the annular conductive layer 4 and to the gear-pattern conductive layer 3 through conductors embedded beneath an insulative film layer placed over the surface of the contact disk 1, and the terminal part 6 is electrically connected to the internal gear-pattern conductive layer 2 at the surface of the contact disk 1, respectively. Terminals 8, 9 and 10 are electrically connected to the terminal parts 5, 6 and 7, respectively. Regions 11a, 11b, 11c and 11d of the surface of the contact disk 1 other than those occupied by the conductive layers are coated with the insulative film layers.
Numerals 12a' and 12b' indicate spots of the surface of the contact disk 1 over which the tips 12a and 12b of brush 12 are contacting with the conductive layers 2, 3 and 4. The mode of this contacting of the tips 12a and 12b of the brush 12 is shown in a partly cut-out perspective view of FIG. 2. The brush 12 is designed to be able to rotate about an axis which shares the center 13 of the contact disk 1 while its tips 12a and 12b are contacting with the conductive layers 2, 3 and 4. During the rotational movement of a knob attached to the brush 12, the tip 12b of the brush 12 touches upon and separates from the teeth parts 2a and 3a of the gear-pattern conductive layers 2 and 3, one after another.
In the above structured rotary encoder contact disk combined with a circuit 14 shown in FIG. 1, let us suppose a situation wherein the brush 12 is rotated in the counterclockwise direction by manipulating a knob (not shown) attached to the brush 12. The results of the measurements made on a voltage waveform across a resistor R.sub.1 (terminals 15a and 15b) and on a voltage waveform across another resistor R.sub.2 (terminals 16a and 16b) will be discussed below.
In FIG. 2, while the tip 12b of the brush 12 touches upon the tooth 2a of the internal gear-pattern conductive layer 2 for a time t.sub.1 by being rotated in the counterclockwise direction, the internal gear-pattern conductive layer 2 is electrically connected with the slip-ring like conductive layer 4 through the tooth 2a, brush tip 12b, brush arm 12 and brush tip 12a for the time t.sub.1. Incidentally, since the internal gear-pattern conductive layer 2 is electrically connected with the terminal 9 on one hand and the slip-ring like conductive layer 4 is connected with the terminal 8 on the other hand, the conduction between the internal gear-pattern conductive layer 2 and the slip-ring conductive layer 4 will result in a short circuit between the terminals 8 and 9 to create a current flowing through the resister R.sub.1 along the direction represented by an arrow in FIG. 1 and a high level voltage across the terminals 15a and 15b for the time t.sub.1 as shown in the upper waveform diagram of FIG. 3a.
Next, during a time t.sub.2 from a time point of separation of the brush tip 12b from the tooth 2a to that of reaching the next tooth 2b, the voltage across the terminals 15a and 15b will be low level as shown in the upper waveform diagram of FIG. 3a, because the connection between the terminals 8 and 9 is open for the time t.sub.2. The upper waveform diagram of FIG. 3a represents the pulse voltage across the terminals 15a and 15b obtained by the succession of the above indicated operations.
On the other hand, the brush tip 12b also contacts with the teeth 3a, 3b, . . . of the gear-pattern conductive layer 3 along with the anticlockwise rotational movement of the brush arm 12. The teeth 3a, 3b, . . . are however slightly shifted in angular position with respect to the teeth 2a, 2b, . . . of the internal gear-pattern conductive layer 2 in the anticlockwise direction, and therefore a current flows through the resistor R.sub.2 in the direction represented by an arrow in FIG. 1 to create a voltage across the terminals 16a and 16b represented by a lower waveform diagram in FIG. 3, in a manner to be slightly delayed as compared with that across the terminals 15a and 15b.
On the contrary, if the knob is rotated in the clockwise direction to cause the brush tips 12a and 12b turn in the same direction, the voltage pulses across the terminals 15a and 15b represented by the upper waveform diagram of FIG. 3b will be delayed as compared with that across the terminals 16a and 16b represented by the lower waveform diagram of FIG. 3b.
As indicated above, by counting the numbers of pulses contained in the voltage waveform which appears across the terminals 15a and 15b and across the terminals 16a and 16b by means of a counter or the like, the angular displacement of the knob can be determined. Furthermore, by comparing the positional relationship between the pulses in the voltage waveforms derived from the partial circuit between the terminals 15a and 15b and from that between the terminals 16a and 16b, the direction of the angular displacement of the knob can be found.
As can be apparent from the illustration of the rotary encoder contact disk, it is one of the most important matter to accurately establish the positional relationship between the radially-arranged teeth of the gear-pattern conduction layer 2 and those of the internal gear-pattern conductive layer 3 on the contact disk 1. If the positional relationship is not accurately established, the positional relationships between the pulse waveforms, shown in FIGS. 3a and 3b, respectively, are also impaired to unable the accurate determination of the rotational direction of the rotating knob. Incidentally, the larger the members of the radially-arranged teeth of the gear-pattern conductive layer 2 and 3 and the smaller the periods of pulse output from the encoder are selected, the more accurately can an angular position of the knob be determined. An accurate establishment of the positional relationships between the teeth of the conductive layers 2 and 3 will, however, become increasingly difficult with the increase of the number of the teeth.
In the past, in printing the gear-pattern conductive layers 2 and 3 on the contact disk 1 by means of screen printing process, the both patterns have been printed independently as will be elucidated in the following description referring to FIGS. 4a through 4e inclusive, each of which shows respective steps of the consecutive process. This mode of the printing process is however liable to cause a shear and/or short circuit defect between the teeth. Furthermore, this mode of the process requires a lot of repeated printing steps for forming conductive layers and insulative layers of given pattern. The conventional process will be described by referring to FIGS. 4a through 4e inclusive.
The conventional screen printing process will first be summarized as follows.
(1) Preparing a flat screen having a multiplicity of fine pores evenly over the whole surface thereof, and filling-up the pores in a region other than a region corresponding to the pattern to be printed, with a region or the like paint stopping substance,
(2) Applying this flat screen to a substrate on which the pattern is to be printed, and
(3) Applying a conductive paint comprising silver powder and the like on a metal mesh laminated on the flat screen and pressing the paint to the flat screen to allow the silver powder paint pass through the pattern region of the flat screen wherein the pores are not filled-in with the resin and let the powder adhere to the surface of the substrate to form a conductive layer of the given pattern.
A process similar to that indicated above can also be performed for forming an insulative layer on the substrate by printing with insulative powder paint on a layer of conductive substrate.
Substrate of a contact disk 1 shown in FIG. 4a is made by cold-press molding of powder of synthetic resin. A slip-ring like conductive layer 4 and a terminal part 5 shown as a hatched part for clarification of pattern in the figure are printed by means of the screen printing process with a conductive paint comprising silver powder or the like at the same time. The slip-ring like conductive layer 4 is electrically connected with the terminal part 5 through a midway part 5c.
In the step shown in FIG. 4b, an insulating layer 17 shown as a fine dotted part in the figure is printed thereon to cover the midway part 5c with the layer 17. The slip-ring pattern conductive layer 4 and the terminal part 5 remain to be exposed after the insulating layer is placed. In the step shown in FIG. 4c, the gear-pattern conductive layer 3 and the terminal part 7 which are shown as hatched parts in the figure are printed by means of the screen printing process. The gear-pattern conductive layer 3 is electrically connected with the terminal part 7 through a midway part 7c formed as continuous part thereto.
In the step shown in FIG. 4d, the midway part 7c is coated with an insulative film 7d. Thereafter, in the step shown in FIG. 4e, the internal gear-pattern conductive layer 2 and the terminal part 6 shown as a hatched part of the figure are printed, simultaneously. Next, as shown by FIG. 1, terminals 8, 9 and 10 are provided on each of the terminal parts 5, 6 and 7 to complete the contact disk.
As indicated above, the conventional method for preparing the contact disk requires the five printing steps; that is, the conductive layer or the insulative layer is printed in the respective steps indicated in each of FIGS. 4a-4e. Furthermore, since the gear-pattern conductive layer 3 and the internal gear-pattern conductive layer 2 are printed independently at the steps shown respectively in FIG. 4c and FIG. 4e, the obtained contact disk is liable to the defects in, for example, a shear in the relative position of the patterns and a short circuit between the teeth.